1. Field of the Invention
This invention relates generally to a method and apparatus for recording a digital information signal and, more particularly, relates to a method and apparatus for recording a digital information signal and a pilot signal using a rotary head and employing the pilot signal to control tracking alignment of the rotary head during playback.
2. Description of the Prior Art
When a video signal and an audio signal are recorded on a magnetic tape using a helical-scan rotary head to form slanted tracks, it is known that the video signal and audio signal can be advantageously reproduced if they are recorded in pulse-code modulated (PCM) form.
In this case, tracking control for controlling the rotary head to accurately trace the recorded tracks upon playback is typically carried out by using a control signal that has been recorded along one edge of the magnetic tape by a fixed head. This control signal is reproduced by a fixed head during the reproduction mode and the reproduced control signal and the rotary phase of the rotary head are maintained in constant phase relation.
This known tracking control method requires the use of a special fixed magnetic head and such fixed magnetic head is a disadvantage in compact equipment, because it requires its own mounting space in the recording and reproducing apparatus.
One approach to overcoming the use of the fixed head is a proposed tracking control method that does not use such fixed magnetic head but uses only the reproduced output signal from the rotary magnetic head to carry out the tracking control for the rotary head. This tracking control method is disclosed in, for example, U.S. patent application Ser. No. 06/584313 filed Feb. 28, 1984 and assigned to the assignee hereof. This tracking control method relies upon the fact that it is easy to time-compress and time-expand the PCM signal and also that it is not necessary to record and reproduce the PCM signal continuously, unlike an analog signal. Hence, the PCM signal and another different signal can easily be recorded on separate regions of each of the plurality of slanted tracks formed during recording.
When the PCM signal is time-compressed and magnetically recorded by a plurality of rotary heads to form the slanted tracks with no guard bands between adjacent tracks, a plurality of tracking control pilot signals are recorded in the longitudinal direction in each track to form a record region independent from the record region for the PCM signal. Upon playback the recorded track is traced by the rotary head having a tracing width greater than the track width, and the tracking of the rotary head is controlled by the pilot signals reproduced from the tracks adjacent the track being traced by the rotary head.
As a reference signal for the tracking control pilot signal a pulse signal (PG) having a frequency of 30 Hz is used that is indicative of the rotary phase of the head and that is generated in synchronism with the rotation of the motor that drives the rotary head.
Nevertheless, during playback when the pulse signal PG is used as a position detecting reference when the tracking pilot signal is reproduced, the reference position of the pulse signal PG can be altered or displaced due to mechanical and electrical variations in the parameters of the apparatus, caused by changes in temperature and the environment, and such variations appear as a kind of tracking error constant (offset) upon playback.
As a result, upon playback, it becomes difficult to reproduce the tracking pilot signal with the same timing as that which was present during recording, and control of the rotary head becomes imprecise. This provokes a particular disadvantage because it becomes impossible to achieve compatibility among individual units of the same kind of apparatus.
Furthermore, because the sampling pulse that is used to reproduce the tracking pilot signal over one rotational period of the rotary head is formed with the pulse signal PG as a reference, the amount of error present therein becomes integrated, so as to be increased by so-called jitter and the position of the sampling pulse is displaced in time.
Moreover, in any tracking control system for use with such recording and reproducing apparatus, not only the normal playback mode must be considered but also variable tape-speed playback modes, in which the tape speed is different from that of the recording mode, must be taken into consideration.